Mountain-Size Asteroid to Fly by Earth Monday: How NASA Will Watch

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A mountain-size asteroid will zoom past Earth Monday (Jan. 26),
marking the closest pass by such a large space rock until 2027.

Asteroid 2004 BL86, which is about 1,800 feet (550 meters)
wide, will come within 745,000 miles (1.2 million kilometers) of
our planet Monday — about three times the distance between
Earth and the moon. While this flyby poses no threat to Earth, it
does present a rare opportunity to get a good look at a
near-Earth asteroid, NASA officials say.

Scientists are eager to study 2004 BL86 to pinpoint its orbit,
observe its surface and even look for moons. The plan is to track
the fast-moving asteroid using the 230-foot (70 m) dish-shaped
Goldstone antenna at NASA's Deep Space Network in California, as
well as the 1,000-foot (305 m) Arecibo Observatory in Puerto
Rico. These radio dishes will beam microwave signals at the
asteroid, which will then bounce off the target and return to
Earth. [ Photos:
Potentially Dangerous Asteroids ]

"For objects that get this close, that are this large, the radar
observations are really analogous to a spacecraft flyby in terms
of the caliber of the data that we can get," said Lance Benner of
NASA's Jet Propulsion Laboratory in Pasadena, California, who is
the principal investigator for the Goldstone observations of the
asteroid.

The resulting black-and-white images can reveal unprecedented
details about
asteroids, whereas most ground-based telescopes would see
only a point of light. But the first item on the team's checklist
will be to nail the space rock's location in space and time. This
will enable a better understanding of the object's orbit and its
future motion, scientists say.

Even though 2004 BL86 poses no threat to Earth for the
foreseeable future, it's still a good idea to keep a close eye on
the asteroid, Benner said.

"Really, it's an inexpensive form of insurance to monitor these
objects on a regular basis," he told Space.com.

Benner also postulates that such work will benefit commercial
companies that plan to visit and mine
asteroids in the future.

The researchers expect to obtain resolutions as fine as 13 feet
(4 m) per pixel, so the images of 2004 BL86 should reveal details
as small as the length of a typical car. This will allow the
scientists to assess how rugged or smooth the space rock's
surface is.

"It's expected to be one of the best radar-imaging targets of
this calendar year," Benner said.

If Benner and his colleagues get enough images as the object
spins, they can start to reconstruct its three-dimensional shape
in order to understand how it rotates. They also plan to search
for any moons in tow. About 17 percent of asteroids in 2004
BL86's size range tend to have smaller objects trailing along
with them.

The Goldstone antenna will track the asteroid for 5 to 6 hours
most nights from Jan. 27 to Feb. 1. The Arecibo
Observatory, however, will only be able to spot 2004 BL86 on
the night of Jan. 27. Its radar is not fully steerable, and the
space rock will be zipping through the sky at 2 degrees (roughly
four times the width of the moon) per hour.

"The thing that excites us the most is that we don't know
anything about it, but it's likely that we'll learn a great deal
and see a lot of detail," Benner said. "Whenever one of these
objects comes really close like this, it offers such an
outstanding opportunity — we almost always see things we haven't
seen before. And so we're expecting some kind of surprise."

Editor's note: If you capture a telescope view
of asteroid 2004 BL86 during its flyby and want to share it with
Space.com, you can send images and comments to managing editor
Tariq Malik at: spacephotos@space.com.